Physician Focus: To catch a thief

Dr. M. Lisa McHam

Monday

Dec 24, 2007 at 12:01 AMDec 24, 2007 at 6:04 PM

Even in the United States, where diagnosis and treatment are widely available, many patients will already have advanced glaucoma when they are first diagnosed. Estimates are that 3 million Americans have the condition, but only half are aware of it.

It's called the ``sneak thief of sight,'' because the vision loss it causes is slow, painless and irreversible. It is glaucoma, a leading cause of blindness around the world.

Even in the United States, where diagnosis and treatment are widely available, many patients will already have advanced glaucoma when they are first diagnosed.

Estimates are that 3 million Americans have the condition, but only half are aware of it.

Glaucoma is a disease that damages the optic nerve. When this nerve, which transmits images captured by the eye to the brain, becomes impaired, the field of vision gradually constricts, often at different rates in the two eyes. Since most vision screening tests measure only the fine central vision, these tests can remain normal until late in the course of the disease. The result is by the time a person notices vision problems from glaucoma, he or she already has serious vision loss.

The biggest and best understood culprit in glaucoma-related optic nerve damage is eye pressure. The higher the pressure, the more likely glaucoma will develop. Eye pressure is controlled primarily by a sieve-like drain in the part of the eye called the angle, where the iris meets the internal wall of the eye. Fluid is continuously made by a pump inside the eye, and if the drain does not function properly, fluid builds up and eye pressure will increase. The increased pressure can damage the optic nerve, causing loss of vision.

Two main types of glaucoma exist: open angle and closed angle. The most common is open angle, where the drain appears normal but the pressure is too high for the health of the eye. With closed angle, the iris is too close to the drain and actually blocks it. This blockage can occur suddenly, resulting in a rapid increase in eye pressure with symptoms of blurred vision and severe eye pain. This condition should be regarded as a medical emergency.

In most cases, elevated eye pressure is the major factor causing damage. Optic nerve damage can occur, however, when eye pressure is only slightly elevated or even high-normal. In these cases, additional factors are involved, including poor circulation to the nerve and other biochemical and genetic factors.

Glaucoma is more common as people age and in persons of African or Hispanic descent. African-Americans are five times more likely to develop glaucoma and six times more likely to go blind from it than their European-descended counterparts.

African-American men, in particular, tend to develop glaucoma at a younger age, often in their 40s. Family history, strong eyeglasses correction, previous eye trauma and the use of steroids are also known risk factors.

Diagnosis is best made with a comprehensive eye exam by an ophthalmologist, a doctor who specializes in the eye. If any findings suggest the possibility of glaucoma, the patient will undergo further tests, usually including a peripheral vision test, an optic nerve photograph and other imaging tests of the nerve.

Different treatment options are available for glaucoma patients, with the goal of lowering eye pressure. Even where the pressure is only high-normal, lowering it can reduce the risk or progression of vision loss. Many patients can have their eye pressure controlled with a well-tolerated, once-a-day eyedrop. A new form of laser treatment is also being used to lower eye pressure earlier in the course of the disease. A small number of patients with hard-to-control glaucoma may need more invasive surgical procedures.

As a physician who treats patients with glaucoma every day, I urge everyone 40 or older to undergo a comprehensive eye examination, as recommended by the American Academy of Ophthalmology. Sadly, too many cases of this common eye disease are still diagnosed in their late states when saving vision can be challenging.

The good news is that most glaucoma-related blindness is preventable with early detection, when treatment is easiest and most effective. You've only got two eyes; do whatever you can to keep them healthy.

For more information about glaucoma and eye health, visit the National Eye Institute at www.nei.nih.gov/health/glaucoma.

M. Lisa McHam, M.D., is president of the Massachusetts Society of Eye Physicians and Surgeons and chairman of the Public Health and Education Committee of the New England Ophthalmological Society. Physician Focus is a public service of the Massachusetts Medical Society. Readers should use their own judgment when seeking medical care and consult with their physician for treatment. Send comments to PhysicianFocus@mms.org.